I think you still have to have an account (last time I used it anyway), but you're right, there is a tier you don't have to pay any money for. It's just an email address but whatever. You can use it via their website but afaik they haven't released a free model based on the data they've scraped off us, so you can't host it on your own hardware and properly do what you want with it. I have heard though that commercial websites were/are using ChatGPT bots for customer service and you can easily use the customer service chatbots on their website to do other random stuff like writing bash scripts or making yo mama jokes.

Open access != Copyleft, but its a decent start.